A voltage-controlled current source, such as a transconductance amplifier, may convert a difference between voltages to current. The ideal transfer characteristics of a transconductance amplifier is:Iout=Gm(Vin+−Vin−),where                Iout is current at the output of the amplifier,        Gm is the transconductance,        Vin+ is voltage at the non-inverting input of the amplifier, and        Vin− is voltage at the inverting input.        
Hence, the transconductance amplifier produces an output current proportional to a difference between voltages at its inputs. The most simple transconductance amplifier consists of a differential pair to convert the input voltage difference to two currents I+ and I−. These currents are then mirrored to the output so that their difference becomes the output current of the amplifier. Hence, the transconductance amplifier should produce zero net output current, when the same voltages are applied to its inputs.
However, an offset voltage associated with amplifier circuitry itself may affect the output current of the transconductance amplifier. For example, the offset voltage may be caused by dynamic conditions, such as thermal, light and radiation conditions, by differences in the size of the input stage transistors, by differences in the doping and base diffusion of these transistors, by current mirror inaccuracies, and other circuitry imperfections. Due to the offset voltage, the transconductance amplifier may produce some current at its output even when voltages applied to its inputs are the same.
Therefore, there is a need in an offset correction or autozero circuit that would compensate for the offset voltage to produce a correct current value at the output of the transconductance amplifier.